Metformin hydrochloride (MFH) is an oral anti-diabetic drug of biguanide class. Two selective spectrophotometric methods were presented for the determination of MFH in pharmaceuticals. The methods were based on the measurement of yellow-coloured charge-transfer complexes formed between MFH and two poly-nitrophenols, namely, 2,4-dinitrophenol (DNP method, at 405 nm) and picric acid (PA met...